1. Field of the Invention
The present invention relates generally to motor lamination stacks and, more particularly, to cooling passages in motor lamination stacks.
2. Description of the Related Art
In conventional motor fabrication techniques, rotor and stator cores are formed by stacking laminations of iron or steel. Each lamination has holes which may be used for insertion of motor windings, insertion of through-bolts, or application of cooling air, for example. Lamination holes are generally formed by mechanical punching, and can also be formed using lasers or chemical etch solutions.
The winding holes are typically referred to as winding "slots" which either can be situated entirely within the lamination or can have one portion extending open to an outer edge of the lamination. The winding slots and through-bolt holes are stacked so as to be aligned with smooth surfaces to ease in the insertion of respective coils and bolts with minimum wasted space for clearance.
Smooth surfaces, however, are detrimental for holes used as air passages for cooling the motor because smooth surfaces provide stable and streamlined airflow. Good heat transfer requires turbulent boundary layers and efficient mixing of air at the boundary layer surface with air in the bulk flow of the cooling stream.
Turbulence can be achieved by roughening the surfaces of the passages. In earlier motor applications, when tolerances on laminations were less precise, a stagger in the lamination stacking resulted naturally in rough passage surfaces and adequate heat transfer occurred. This natural stagger is not an option in conventional motor fabrication techniques that require precise punchings of holes for the winding and through-bolt passages. In these conventional techniques, to provide irregular cooling passage surfaces, extra roughening steps are required to treat the cooling passage surfaces.